Safety jack with auxiliary safety nut



April 6, 1965 M, s'ruR 3,176,963

SAFETY JACK WITH AUXILIARY SAFETY NUT Filed March 23, 1962 2 ShetsJ-Sheet 1 10b 26 J J as INVENTOR.

eoBeerm. STUEM J15. 2

" www A ril 6, 1965 R. M. STURM SAFETY JACK WITH AUXILIARY SAFETY NUT 2 Sheets-Sheet 2 Filed March 23 1962 Q x x X m INVENTOR. E05EE7'M STUEM %1 H15 flTTOENE'VS United States Patent Filed Mar. 23, 1962, Ser. No. 181,874 3 Claims. or. 254-102,

This invention relates to jacks and more particularly those types of jacks commonly known as worm gear screw jacks. However, the invention is not necessarily so limited.

An object of this invention is to provide an indicator for warning the users of worm gear screw jacks and the like that portions of the jack are becoming so worn as to render further operation of the jack undesirable.

A further object of this invention is to provide a safety device for worm gear screw jacks and the like, providing an auxiliary support for a threaded jack screw in the event the primary support for the jack screw should fail.

Other objects and advantages reside in the construction of parts, the combination thereof, the method of manufacture and the mode of operation, as will become more apparent from the following description.

Referring to the drawings,

FIGURE 1 is a perspective view of a preferred embodiment of a worm gear screw jack made in accordance with this invention.

FIGURE 2 is a partial, longitudinal cross-sectional view of a portion of the jack of FIGURE 1. FIGURE 2 shows the parts of the screw jack just after assembly.

FIGURE 3 is a partial cross-sectional view similar to FIGURE 2 showing the parts of the jack after the jack has been used for a considerable length of time.

FIGURE 4 is a partial cross-sectional view similar to FIGURE 2 illustrating parts of the jack after such long continued use that portions of the jack have failed.

FIGURE 5 is a partial sectional view taken along lines 5-5 of FIGURE 4.

FIGURE 6 is a perspective View of a connecting ring used in the jack.

Referring to the drawings in greater detail, a jack made in accordance with this invention is shown as including a hollow housing 10 having cylindrical portions Ilia and ltlb arranged at right angles to one another for receiving the various working parts of the jack. A base or mounting plate portion 100 is formed integral with the portions 16:: and 1012 such that the portion 19a projects vertically upwardly when the plate portion 100 is attached to a horizontal surface. It will be appreciated, however, that the portion 100 could be attached at surfaces extending at various angles to the horizontal.

Supported on the base of the housing portion 10a by means of a lower thrust bearing 12 is :a drive nut 14 having internal threads engaging and supporting a jack screw 16. For convenience, the orientation of the jack screw 16 will be designated as vertical herein. Of course, the orientation of the jack screw 16 depends entirely upon the manner used and, for example, could be horizontal as well as vertical. The top of the jack screw 16 projects upwardly through a central aperture located within a housing cap 18 while its lower portion depends into a protection tube 20 attached as by a threaded connection 22 to the bottom of the housing portion 100. The screw 16 is adapted to engage and move a load (not shown) in an axial direction and for this purpose may be provided with a load engaging pad 24 at its upper end.

The nut 14, which is concentric with the axis of rotation of the jack screw 16, is confined between the aforementioned thrust bearing 12 and an upper thrust bearing 26. The bearings 12 and 26 are received within recesses in 3,136,953 Patented Apr. 6, 1965 "ice the housing portion and the base of the housing cap 18 respectively. It is to be understood that the bearings 12 and 26 are conventional thrust bearings including ball elements caged in any suitable manner. The nut 14 is provided with hub portions 28, 30 projecting upwardly and downwardly respectively and received within central apertures formed within the thrust bearings 26 and 12.

The operation of screw jacks of this type is believed obvious to those skilled in the art. Normally, the load engaging pad 24 or its equivalent element is so attached to or otherwise engaged with the load that rotation of the jack screw 16 is prevented. The drive nut 14 is provided with concave external worm gear threads 32 which are engaged by a worm 34 mounted in the housing portion 101: on a worm shaft 36 disposed in right angular relationship to the direction of travel of the screw 16. The worm shaft 36 may be supported within the housing portion 10b in conventional fashion by bearings (not shown) located adjacent to bearing caps 38 afiixed as by oap screws 40 to the housing portion 1%. Upon rotation of the worm 34, the nut 14 will be rotated relative to the housing 10 and the jack screw 16 since the jack screw 16 is held against rotation and must move axially relative to the nut 14. The jack shown in the drawings is so designed that clockwise rotation of the nut 14 drives the jack screw 16 vertically upwardly thereupon driving the load upwardly.

Although screw jacks of this type are highly successful in operation, it is apparent that there will be considerable wear of the internal screw threads on the nut 14. As a practical matter, it is impossible to make the internal threads of the nut 14 with such precision that there is no backlash when the screw jack is first assembled. Further, since the internal threads of the nut 14 not only drive, but also support the jack screw 16 and a load carried thereby, the internal threads of the nut 14 wear rapidly. After long continued use of the screw jack, the internal threads of the nut 14 may become so worn that they no longer are capable of supporting the jack screw 16. In such event, the screw 16 and the load supported thereby may drop a considerable distance until the pad 24 strikes the top of the cap 18 or some other element breaks the fall of the screw 16. Since screw jacks often are engaged with heavy loads, failure of the nut 14 not only may result in injury to the load and the remainder of the jack, but also can endanger anyone near the jack.

In accordance with this invention, indicator means are provided so that the user of the screw jack can visually determine that the internal threads of the nut 14 are becoming dangerously worn. For convenience, the indicator means projects out of the housing so that no disassembly of the screw jack is required and wear of the nut 14 can be determined at a distance from the jack. In addition, should the threads in the nut 14 become so worn as to be no longer capable of supporting the screw 16, means are provided forming a part of the indicator means to maintain support of the jack screw 16.

As shown in FIGURE 2, the indicator means comprises an auxiliary nut 42 having internal threads in engagement with the threads of the screw 16. The nut 42 is mounted concentric with the screw 16 and spaced above the drive nut 14. The auxiliary nut 42 is received within the central aperture in the housing cap 18 and the top portion of the nut 42 projects thereabovc when the unit is first assembled. The bottom of the auxiliary nut 42 is provided with an enlarged bored or cut-out portion receiving a connecting ring 44 which is attached thereto by means of pins 46 projecting through aligned apertures in the ring 44 and the auxiliary nut 42. The ring 44 is shown in perspective view in FIGURE 6, wherein the apertures within the ring are designated by reference character 48. A pair of diametrically opposed depend- 3 ing tangs 50 project beneath the auxiliary nut 42 into a pair of aligned slots in the hub portion 28 of the nut 14. The slots, only one side 52 of which are seen in the crosssectional view of FIGURE 2, are of only slightly greater width than the tangs 50. Accordingly, there can be no appreciable relative rotation between the drive nut 14 and theauxilia-ry nut 42. Since there can be no relative rotation between the'two nuts 14 and 42, there is ordinarily no axial "motion between these nuts. However, when the unit is first assembled, the bases of the tangs 50 are located above the bases of the slots located in the hub portion 28. Consequently, lowering of the jack screw 16 caused by wear of the internal threads of the nut14 will result in an axial lowering of the nut 42 relative to the nut 14. Since the'nut 42 is not connected to the nut 14 other than by the connecting ring 44, the nut 42 does not serve as a support for the screw 16 in normal operation. For this reason, there is only a slight wearing of the internal threads of the nut 42 as compared to the wearing of the internal threads of the nut 14.

The auxiliary nut 42 functions as follows. device is first assembled, the parts occupy the relationship shown in FIGURE 2 wherein the top surface of the nut 42 projects a slight distance above the top surface of the cap 18. As the internal threads of the drive nut 14 become. worn, the jack screw 16 lowers, carrying the auxiliary nut 42 with it. After prolonged use, the parts will occupy the position shown in FIGURE '3 wherein the top surface of the auxiliary nut 42 is coplanar with the surrounding top surface portion of the housing cap 18. Note in FIGURE 3 that the internal threads ofthe drive nut 14 are'so badly worn as to be only half or less of their original thickness. Further operation of the screw jack shown in FIGURE 3 would not be recommended. It is apparent then, that the user of the jack need only inspect the top'of the jack housing to see whether the nut 42 projects above the housing If it does not project above the housing, the user thereby is warned that further operation of the jack is undesirable and that the nut 14 should be replaced.

In FIGURE 4, the parts of the jack are shown when the internal threads of the nut 14 have'become so worn that they are no longer capable of supporting the screw 16. While the internal surface of the drive nut 14 is shown as smooth, it will, of course, be appreciated that in practice such a smooth wearing of the internal threads of the nut 15 would not occur. However, it is possible for the threads to be so worn that the weight of the screw 16 and the load carried thereby can shear ofi portions of the threads or, if the threads of the screw 16 are slightly worn, the mating threads of the nut 14 and screw 16 will no longer be in supporting engagement. Note in FIGURE 4 that the auxiliary nut 42 has dropped so that its top surface is considerably below the top surface of the housing cap 18. Note also that, although the internal threads of the drive nut 14 are no longer capable of supporting the screw 16, the internal threads of the auxiliary nut 42, which now rest upon the nut 14, are capable of supporting the screw 16. Accordingly, there is no appreciable drop of the screw 16. even when the internal threads of the drive nut 14 can no longer support the screw 16.

If the pins 46 were sufliciently strong, the jack would remain operable even though the internal threads of the drive nut 14 are sheared smooth. This would greatly increase the life of the screw jack and such a strong connection between the auxiliary nut 42 and the drive nut 14 is recommended where long life of the jack is desired. However, it is believed more important that the screw jack'be rendered inoperative when the drive nut 20 When the 14 no longer is capable of supporting the screw 16. This is accomplished by using pins 46 which are sufliciently.

weak that they will shear under the Weight of the load when the drive nut 14 is rotated to move the load. As shown in FIGURES 4 and 5, the pins 46 shear so that the ring 44 rotates with the drive nut 14 relative to the auxiliary nut 42. The auxiliary nut thus does not rotate once the pins 46 have sheared.

From the foregoing description, it is seen that the objects of the invention have been satisfied. So long as the internal threads of the drive nut 14 can support the screw 16, the screw 16 effectively supports the auxiliary nut 42. Since the auxiliary nut 42 rotates in unison with the drive nut 14, the position of thenut 42 relative to the housing 10 is dependent upon the Wear of the internal threads of the nut 14. When the internal threads of the nut 14 can no longer support the screw 16, the screw and the nut 42 lower so that the nut 42 rests upon the nut14. The nut 42 then supports the screw 16. Accordingly, the nut 42 serves as an indicator of the wear of the internal threads of the drive nut 14. Thereafter,

if the nut 14 is rotated in an effort to drive the screw. Although further operation of, the jack is impossible, the screw 16 and the load carried, thereby are safely supported.

16, the pins 46 shear.

Although the preferred embodiment of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described'rny invention, I claim:

1. In a screw jack, a fixed support; a drive nut havmg internal threads mounted for rotation on said sup port; a threaded jack screw projecting through said nut and supported by said internal threads; an auxiliary nut having internal threads engaged with said screw spaced above said drive nut; a ring having an upper portion received within a lower surface portion of said auxiliary nut and connected thereto by at least one pin projecting between said ring and said auxiliary nut, said ring havmg at least one depending tang projecting into a slot 7 formed in the top surface of said drive nut whereby said ring andsaid auxiliary nut rotate along with said drive nut, the bottom surface of said tang being spaced above the base of said slot when the screw jack is initially assembled, whereby said jack screw and said auxiliary nut may lower relative to said fixed support as the in-- port comprises a. housing enclosing the drive nut and a portion of said jack screw, said auxiliary nut being located within an aperture in said housing, whereby wear of the threads in said drive nut is indicated by the position of said auxiliary nut relative to said housing.

References Cited by the Examiner UNITED STATES PATENTS 786,35 3 4/05 Gabriel.

FOREIGN PATENTS 652,199 4/51 Great Britain.

WILLIAM FELDMAN, Primary Examiner. HARRISON R. MOSELEY, Examiner. 

1. IN A SCREW JACK, A FIXED SUPPORT; A DRIVE NUT HAVING INTERNAL THREADS MOUNTED FOR ROTATION ON SAID SUPPORT; A THREADED JACK SCREW PROJECTING THROUGH SAID NUT AND SUPPORTED BY SAID INTERNAL THREADS; AN AUXILIARY NUT HAVING INTERNAL THREADS ENGAGED WITH SAID SCREW SPACED ABOVE SAID DRIVE NUT; A RING HAVING AN UPPER PORTION RECEIVED WITHIN A LOWER SURFACE PORTION OF SAID AUXILIARY NUT AND CONNECTED THERETO BY AT LEAST ONE PIN PROJECTING BETWEEN SAID RING AND SAID AUXILIARY NUT, SAID RING HAVING AT LEAST ONE DEPENDING TANG PROJECTING INTO A SLOT FORMED IN THE TOP SURFACE OF SAID DRIVE NUT WHEREBY SAID RING AND SAID AUXILIARY NUT ROTATE ALONG WITH SAID DRIVE NUT, THE BOTTOM SURFACE OF SAID TANG BEING SPACED ABOVE THE BASE OF SAID SLOT WHEN THE SCREW JACK IS INITIALLY ASSEMBLED, WHEREBY SAID JACK SCREW AND SAID AUXILIARY NUT MAY LOWER RELATIVE TO SAID FIXED SUPPORT AS THE ININTERNAL THREADS OF SAID DRIVE NUT BECOME WORN. 